This project proposes to investigate changes in post-traumatic stress disorders (PTSD) under conditions of psychotherapeutic treatment, using psychophysiological, endocrinological, and behavioral variables as objective markers. It is hypothesized that a) PTSD symptomatology results from failure to process the emotional concomitants of traumatic events, b) successful processing requires that activation of the unprocessed emotions, c) this activation can be accomplished through the means of imaginal exposure (flooding) and tracked by measuring associated physiological, endocrinological, and behavioral responses, and d) gradual reduction (habituation) of these responses within and across exposure sessions predicts positive treatment outcome. The project also proposes to investigate whether utilization of the flooding technique as a probe can improve discrimination between PTSD and non-PTSD subjects. Subjects will be medication-free male Vietnam combat veterans, with and without PSTD. Each PTSD subject will undergo two series of imaginal exposure (flooding) therapy sessions, one for each event that formed the basis for a traumatic combat script developed in a previous Assessment Procedure. Therapy sessions will be conducted in the laboratory, where heart rate, skin conductance, and three facial EMG levels will be continuously recorded. Blood samples will be collected during desginated flooding sessions for serum cortisol and plasma epinephrine, norepinehrine, ACTH, beta-endorphin, arginine vasopressin, and growth hormone. Designated sessions will be videotaped for quantification of subject behaviors. A battery of outcome variables will be assessed prior to and following each flooding series and at six-month and one-year follow-ups. Tonic level, activation, and within-and between-session habituation of the physiological, endocrinological, and behavioral measures obtained during flooding sessions will be employed as predictor variables treatment outcome, utilizing stepwise multiple regression and canonical correlation analytic techniques. Control subjects will undergo one flooding session only, during which the dependent measures will be obtained in the same manner as for the PTSD subjects. The ability of physiological, endocrinological, and behavioral responses to distinguish PTSD and Control subjects will be assessed via MANOVA and discriminant analytic techniques.